Gliederung

Aim: Targeted radiotherapy of bone marrow with radiolabelled monoclonal antibodies is a therapeutic approach of considerable potential for the treatment of relapsing leukemias for escalating conditioning prior to stem cell transplantation. Beta-irradiation induces apoptosis and activates apoptosis pathway involving the CD95 receptor/CD95 ligand system in leukemia cells in vitro. However, the mechanisms by which beta-irradiation induces cell death during RIT in vivo are not well understood at the molecular level.

Methods: Peripheral blood lymphocytes (PBLs) were isolated from patients treated with 5 GBq of Y-90 labelled anti-CD45 monoclonal antibodies ([Y-90]anti-CD45). After 2, 4, 8, and 24 h induction of DNA damage in PBLs was assessed using Comet-assay and activation of apoptosis pathways in PBLs was performed using Western blot analysis.

Results: [Y-90]anti-CD45 induces DNA-damage, activates caspases, increases pro-apoptotic proteins and downregulates anti-apoptotic proteins in peripheral blood lymphocytes (PBLs) during RIT. Upregulation of death-inducing ligands (DIL) and receptors (DIL-R) such as CD95 were found in PBLs isolated from patients during RIT with [Y-90]anti-CD45 after 2 h. In addition, activation of caspases-8 and caspase-3 and PARP cleavage were detected in isolated PBLs during RIT after 2 h. In addition, we found that caspase-9 was activated, indicating that activation of mitochondria were involved during RIT with [Y-90]anti-CD45. Bax and Bcl-xS, death-promoting proteins, were upregulated and Bcl-xL, a death-inhibiting protein, was downregulated. Furthermore, we found a strong upregulation of p21, which was involved in cell cycle arrest.

Conclusions: It is shown that [Y-90]anti-CD45 induces DNA-damage, p21-mediated cell cycle arrest and activates extrinsic and intrinsic apoptosis pathways in PBLs. Targeted radiotherapy of bone marrow with radiolabelled monoclonal antibodies is a therapeutic approach of considerable potential for the treatment of relapsing leukemias for escalating conditioning prior to stem cell transplantation. Upregulation of CD95 ligand/receptor system will sensitize leukemic cells to cytotoxic effects of additional anticancer treatment.